Polyolefin Gel Processing Composition Containing An Inorganic Acid Scavenger and Method Using Same

ABSTRACT

A polymer composition for producing gel extruded articles is described. The polymer composition contains polyethylene particles combined with a plasticizer and an acid scavenger. In accordance with the present disclosure, the acid scavenger is an inorganic compound that is insoluble in the plasticizer and/or any extractions solvents used during the process. In one embodiment, the acid scavenger is a magnesium aluminum hydroxide carbonate.

RELATED APPLICATIONS

The present application is based upon and claims priority to U.S.Provisional Application Ser. No. 62/647,146, having a filing date ofMar. 23, 2018, which is incorporated herein by reference in itsentirety.

BACKGROUND

Polyethylene polymers have numerous and diverse uses and applications.For example, high density polyethylenes are valuable engineeringplastics, with a unique combination of abrasion resistance, surfacelubricity, chemical resistance and impact strength. They findapplication in the production of high strength fibers for use in ropesand anti-ballistic shaped articles and in the production of otherelongated articles, such as membranes for lithium batteries. However,since the flowability of these materials in the molten state decreasesas the molecular weight increases, processing by conventionaltechniques, such as melt extrusion, is not always possible.

One alternative method for producing fibers and other elongatedcomponents from polyethylene polymers is by gel-processing in which thepolymer is combined with a solvent. The resultant gel is extruded into afiber or membrane, and may be stretched in one or two directions. Also,part or all of the solvent may be removed from the product.

In the past, however, problems have been experienced in gel-processingpolyethylene polymers. For example, polyethylene polymers are typicallymade with Ziegler Natta catalysts that can contain a certain amount ofchlorine. During gel-processing, the chlorine can release from thepolymer as hydrochloric acid. Hydrochloric acid is a corrosive gas thatcan cause damage to processing equipment, such as to the extruder, thepipes, and the like. In the past, in order to prevent acid damage, acidscavengers have been combined with the polyethylene polymer. The acidscavenger reacts with the hydrochloric acid and forms a non-corrosivesalt. A typical acid scavenger widely used in the past for polyethylenepolymers is calcium stearate. Calcium stearate, however, has to be usedin relatively high amounts in order to control the release of acids. Inaddition, calcium stearate is highly soluble in plasticizers andsolvents used during gel processing. During gel processing, theplasticizers and solvents are removed from the final product, collected,and reused. Calcium stearate and other solvent soluble acid scavengers,however, can quickly accumulate within the plasticizer and/or solventand render them unusable.

In view of the above, a need exists for a polyolefin compositionformulated for gel processing that contains a more effective acidscavenger. More particularly, a need exist for an acid scavenger for usein gel processing applications that is highly effective at lowconcentrations and that is not soluble in plasticizers and/or solventsused during the process.

SUMMARY

In general, the present disclosure is directed to polyolefincompositions well suited for gel processing applications. The polyolefincompositions, for instance, can be used to produce elongated articles,such as films, membranes, fibers, and the like. In one embodiment, apolyethylene, such as a high density polyethylene resin, is combinedwith a plasticizer to form a gel-like material. In accordance with thepresent disclosure, the polyethylene resin and plasticizer are furthercombined with an acid scavenger. The acid scavenger is not onlyinsoluble in the plasticizer, but has also been found to be capable ofpreventing acid release within the composition at surprising andunexpectedly low concentrations.

For example, in one embodiment, the present disclosure is directed to apolymer composition for producing gel extruded articles. The polymercomposition comprises a plasticizer blended with polyethylene resin. Thepolyethylene resin can be made from a high density polyethylene, such asa high molecular weight polyethylene. In one embodiment, for instance,the resin is made from an ultrahigh molecular weight polyethylene. Thepolyethylene resin is combined with the plasticizer and an acidscavenger in order to produce a gel-like composition capable of beingextruded. In accordance with the present disclosure, the acid scavengercomprises an inorganic compound that is insoluble in the plasticizer.For example, the inorganic compound may comprise an oxide, a carbonate,a silicate, or mixtures thereof. In one particular embodiment, the acidscavenger comprises a carbonate compound such as an aluminum-sodiumcarbonate. In one particular embodiment, for example, the acid scavengercomprises a hydrotalcite.

As described above, the acid scavenger can be contained in the polymercomposition at extremely low concentrations. For example, the acidscavenger can be present in the composition in an amount less than about250 ppm, such as less than about 200 ppm, such as less than about 150ppm, such as less than about 100 ppm on a weight basis. Even at theabove low concentrations, the acid scavenger can effectively preventacid from being released from the polymer composition during processing.

In general, the polymer composition contains the high densitypolyethylene resin in an amount up to about 50% by weight. Theplasticizer, for instance, can be present in the composition in anamount greater than about 50% by weight, such as in an amount greaterthan about 60% by weight, such as in an amount greater than about 70% byweight, such as in an amount greater than about 80% by weight, such asin an amount greater than about 90% by weight. Various differentmaterials can be used as the plasticizer. For instance, the plasticizermay comprise a mineral oil, a paraffinic oil, a hydrocarbon oil, analcohol, or the like. For instance, the plasticizer may comprisedecaline, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol,oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane,n-dodecane, or mixtures thereof. In one embodiment, the plasticizer maycomprise a C5-C12 hydrocarbon, such as a C5-C12 saturated hydrocarbon.For example, the plasticizer may comprise heptane, hexane, or the like.

In one embodiment, the polyethylene used to produce the particles canhave a relatively high molecular weight. In one embodiment, the use ofhigher molecular weight polyethylene particles may be beneficial,especially in applications where greater strength properties are neededor desired. For example, the polyethylene used to produce the particlescan have a molecular weight of greater than about 500,000 g/mol, such asgreater than about 1,000,000 g/mol, such as greater than about 1,500,000g/mol, such as greater than about 2,000,000 g/mol, such as greater thanabout 2,500,000 g/mol, such as greater than about 3,000,000 g/mol, suchas greater than about 3,500,000 g/mol, such as even greater than about4,000,000 g/mol. In one embodiment, the polyethylene used to produce theparticles comprises a Ziegler-Natta catalyzed ultrahigh molecular weightpolyethylene.

The present disclosure is also directed to polymer articles formed fromthe above polymer composition. The polymer articles can be producedthrough a gel extrusion or gel-spinning process. Polymer articles madein accordance with the present disclosure include fibers, films,membranes, or the like. Because the acid scavenger of the presentdisclosure is not soluble in the plasticizer or in any extractionsolvents used during the process, the acid scavenger remains within thepolymer articles after the articles are formed. In this manner, the acidscavenger remains effective even when the polymer articles are in use.Polymer articles made according to the present disclosure, for instance,can contain the acid scavenger generally in an amount greater than about10 ppm, such as in an amount greater than about 20 ppm, such as in anamount greater than about 30 ppm on a weight basis and generally in anamount less than about 250 ppm.

The present disclosure is also directed to a process for producingpolymer articles. The process includes the steps of forming a gel-likecomposition from the polymer composition described above. The gel-likecomposition is then extruded through a die to form a polymer article.The polymer article, for instance, may comprise fibers, a film, or amembrane. During formation of the polymer article, at least part of theplasticizer is separated and removed from the polyethylene particle. Forinstance, in one embodiment, greater than 80%, such as greater than 90%,such as greater than 95%, such as greater than 98% of the plasticizer isremoved during formation of the polymer article.

In one embodiment, an extraction solvent, such as dichloromethane iscombined with the polymer composition before or during formation of thepolymer article. The extraction solvent can be used to facilitateremoval of the plasticizer. Of particular advantage, the acid scavengerused in accordance with the present disclosure is insoluble not only inthe plasticizer but also in the extraction solvent. Thus, substantiallyall of the plasticizer can be removed from the polymer article withoutalso removing the acid scavenger.

Other features and aspects of the present disclosure are discussed ingreater detail below.

DETAILED DESCRIPTION

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentdisclosure.

In general, the present disclosure is directed to a polymer compositionwell suited for producing gel extruded articles, such as fibers, filmsand membranes. The polymer composition contains a polyethylene resin,such as high density polyethylene particles, combined with a plasticizerand an acid scavenger. In accordance with the present disclosure, theacid scavenger comprises an inorganic compound that is insoluble in theplasticizer and/or in an extraction solvent that may be used during theprocess. In this manner, the acid scavenger does not remain in theplasticizer when the plasticizer is removed from polymer articles and,instead, remains active within the polymer articles for preventing therelease of acid, such as hydrochloric acid. It was unexpectedlydiscovered that the acid scavengers in accordance with the presentdisclosure can be used at extremely low concentrations and still preventacid emissions.

As described above, the acid scavenger for use in the present disclosuregenerally comprises an inorganic compound. The inorganic compound maycomprise an oxide, a carbonate, a silicate, or mixtures thereof. Forinstance, the acid scavenger may comprise a carbonate, such as analuminum-sodium carbonate. In one embodiment, the acid scavengercomprises a hydrotalcite. In one particular embodiment, the hydrotalcitemay have the following chemical formula:

Mg₆Al₂CO₃(OH)₁₆.4(H₂O).

In other embodiments, the acid scavenger may comprise a metal oxide,such as magnesium oxide, zinc oxide, or mixtures thereof. Other acidscavengers that may be used include sodium carbonate, calcium carbonate,other hydroxy metal carbonates, aluminum silicate, and the like.

The acid scavenger, such as a hydrotalcite, may optionally be coated.Example coatings include fatty acids (e.g., higher fatty acids), anionicsurfactants, phosphates, coupling agents, and esters of polyhydricalcohols and fatty acids. Specific examples in some embodiments includehigher fatty acids having 10 or more carbon atoms such as stearic acid,erucic acid, palmitic acid, lauric acid and behenic acid; alkali metalsalts of the higher fatty acids; sulfuric ester salts of higher alcoholssuch as stearyl alcohol and oleyl alcohol; anionic surfactants such assulfuric ester salts of polyethylene glycol ethers, amide-bondedsulfuric ester salts, ester-bonded sulfuric ester salts, ester-bondedsulfonates, amide-bonded sulfonates, ether-bonded sulfonates,ether-bonded alkyl aryl sulfonates, ester-bonded alkyl aryl sulfonatesand amide-bonded alkyl aryl sulfonates; phosphates such as acid andalkali metal salts and amine salts of orthophosphoric acid and mono- ordi-esters such as oleyl alcohol and stearyl alcohol or mixtures thereof;silane coupling agents such as vinylethoxysilane,vinyl-tris(2-methoxy-ethoxy)silane, γ-methacryloxypropyltrimethoxysilane, γ-aminopropyl trimethoxysilane,β-(3,4-epoxycyclohexyl)ethyl trimethoxysilane, γ-glycidoxypropyltrimethoxysilane and γ-mercaptopropyl trimethoxysilane; titanate-basedcoupling agents such as isopropyltriisostearoyl titanate,isopropyltris(dioctylpyrophosphate)titanate,isopropyltri(N-aminoethyl-aminoethyl)titanate andisopropyltridecylbenzenesulfonyl titanate; aluminum-based couplingagents such as acetoalkoxyaluminium diisopropylate; and esters ofpolyhydric alcohols and fatty acids such as glycerin monostearate andglycerin monooleate.

As described above, the acid scavenger can be very effective atpreventing acid emissions within the polymer composition even atextremely and surprisingly low concentrations. For instance, the acidscavenger concentration within the polymer composition can be less thanabout 250 ppm, such as less than about 200 ppm, such as less than about150 ppm, such as less than about 100 ppm, such as less than about 50ppm. In one embodiment, for instance, the acid scavenger concentrationcan be greater than about 20 ppm, such as greater than about 50 ppm, andgenerally less than about 100 ppm, such as less than about 75 ppm on aweight basis.

As shown above, the acid scavengers of the present disclosure have beenfound to be highly efficient in terms of required dosage in order toprevent the formation and/or release of acid from the polymercomposition, such as hydrochloric acid. Having to incorporate lesseramounts of the acid scavenger into the polymer composition leads to lessimpact on polymer processing and on the final polymer properties. Inaddition, the acid scavengers are insoluble in the plasticizer andsolvents used during the process and therefore remain in the polymerproducts and do not build up in the process. By remaining in the polymerproducts, the acid scavengers remain active for preventing the releaseof acids during use of the polymer articles.

In addition to the acid scavenger, the polymer composition of thepresent disclosure for use in gel processing contains a polyolefinresin, particularly a polyethylene polymer in combination with aplasticizer.

As used herein, a polyethylene polymer refers to a polymer made fromover 90% ethylene derived units, such as greater than 95% ethylenederived units, or 100% ethylene derived units. The polyethylene can be ahomopolymer or a copolymer, including a terpolymer, having othermonomeric units. In one embodiment, the polyethylene particles are madefrom a high density polyethylene. A high density polyethylene has adensity of about 0.93 g/cm³ or greater. The polyethylene used to producethe particles can comprise a high molecular weight polyethylene, a veryhigh molecular weight polyethylene, and/or an ultrahigh molecular weightpolyethylene. “High molecular weight polyethylene” refers topolyethylene compositions with weight-average molecular weight of atleast about 3×10⁵ g/mol and, as used herein, is intended to includevery-high molecular weight polyethylene and ultra-high molecular weightpolyethylene. For purposes of the present specification, the molecularweights referenced herein are determined in accordance with theMargolies equation (“Margolies molecular weight”).

“Very-high molecular weight polyethylene” refers to polyethylenecompositions with a weight average molecular weight of less than about3×10⁶ g/mol and more than about 1×10⁶ g/mol. In some embodiments, themolecular weight of the very-high molecular weight polyethylenecomposition is between about 2×10⁶ g/mol and less than about 3×10⁶g/mol.

“Ultra-high molecular weight polyethylene” refers to polyethylenecompositions with weight-average molecular weight of at least about3×10⁶ g/mol. In some embodiments, the molecular weight of the ultra-highmolecular weight polyethylene composition is between about 3×10⁶ g/moland about 30×10⁶ g/mol, or between about 3×10⁶ g/mol and about 20×10⁶g/mol, or between about 3×10⁶ g/mol and about 10×10⁶ g/mol, or betweenabout 3×10⁶ g/mol and about 6×10⁶ g/mol.

As described above, in one embodiment, the polyethylene is a homopolymerof ethylene. In another embodiment, the polyethylene may be a copolymer.For instance, the polyethylene may be a copolymer of ethylene andanother olefin containing from 3 to 16 carbon atoms, such as from 3 to10 carbon atoms, such as from 3 to 8 carbon atoms. These other olefinsinclude, but are not limited to, propylene, 1-butene, 1-pentene,1-hexene, 1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene, 1-dodecene,1-hexadecene and the like. Also utilizable herein are polyene comonomerssuch as 1,3-hexadiene, 1,4-hexadiene, cyclopentadiene,dicyclopentadiene, 4-vinylcyclohex-1-ene, 1,5-cyclooctadiene,5-vinylidene-2-norbornene and 5-vinyl-2-norbornene. However, whenpresent, the amount of the non-ethylene monomer(s) in the copolymer maybe less than about 10 mol. %, such as less than about 5 mol. %, such asless than about 2.5 mol. %, such as less than about 1 mol. %, whereinthe mol. % is based on the total moles of monomer in the polymer.

In one embodiment, the polyethylene may have a monomodal molecularweight distribution. Alternatively, the polyethylene may exhibit abimodal molecular weight distribution. For instance, a bimodaldistribution generally refers to a polymer having a distinct highermolecular weight and a distinct lower molecular weight (e.g. twodistinct peaks) on a size exclusion chromatography or gel permeationchromatography curve. In another embodiment, the polyethylene mayexhibit more than two molecular weight distribution peaks such that thepolyethylene exhibits a multimodal (e.g., trimodal, tetramodal, etc.)distribution. Alternatively, the polyethylene may exhibit a broadmolecular weight distribution wherein the polyethylene is comprised of ablend of higher and lower molecular weight components such that the sizeexclusion chromatography or gel permeation chromatography curve does notexhibit at least two distinct peaks but instead exhibits one distinctpeak broader than the individual component peaks.

In one embodiment, the composition may be comprised of more than onepolyethylene, each having a different molecular weight and/or molecularweight distribution. For instance, the molecular weight distribution maybe within the average molecular weight specifications provided above.

In addition, the composition may be comprised of a blend of one or morepolyethylene polymers or copolymers and another thermoplastic polymersuch as a polypropylene, a polybutylene, a polymethylpentene, a linearlow density polyethylene, or mixtures thereof. However, the amount ofnon-polyethylene polymer(s) in the composition may be less than about 10wt. %, such as less than about 5 wt. %, such as less than about 2.5 wt.%, such as less than about 1 wt. %, wherein the wt % is based on thetotal weight of the composition.

Any method known in the art can be utilized to synthesize thepolyethylene. The polyethylene powder is typically produced by thecatalytic polymerization of ethylene monomer or optionally with one ormore other 1-olefin co-monomers, the 1-olefin content in the finalpolymer being less or equal to 10% of the ethylene content, with aheterogeneous catalyst and an organo aluminum or magnesium compound ascocatalyst. The ethylene is usually polymerized in gaseous phase orslurry phase at relatively low temperatures and pressures. Thepolymerization reaction may be carried out at a temperature of between50° C. and 100° C. and pressures in the range of 0.02 and 2 MPa.

The molecular weight of the polyethylene can be adjusted by addinghydrogen. Altering the temperature and/or the type and concentration ofthe co-catalyst may also be used to fine tune the molecular weight.Additionally, the reaction may occur in the presence of antistaticagents to avoid fouling and product contamination.

Suitable catalyst systems include but are not limited to Ziegler-Nattatype catalysts. Typically Ziegler-Natta type catalysts are derived by acombination of transition metal compounds of Groups 4 to 8 of thePeriodic Table and alkyl or hydride derivatives of metals from Groups 1to 3 of the Periodic Table. Transition metal derivatives used usuallycomprise the metal halides or esters or combinations thereof. ExemplaryZiegler-Natta catalysts include those based on the reaction products oforgano aluminum or magnesium compounds, such as for example but notlimited to aluminum or magnesium alkyls and titanium, vanadium orchromium halides or esters. The heterogeneous catalyst might be eitherunsupported or supported on porous fine grained materials, such assilica or magnesium chloride. Such support can be added during synthesisof the catalyst or may be obtained as a chemical reaction product of thecatalyst synthesis itself.

In one embodiment, a suitable catalyst system can be obtained by thereaction of a titanium(IV) compound with a trialkyl aluminum compound inan inert organic solvent at temperatures in the range of −40° C. to 100°C., preferably −20° C. to 50° C. The concentrations of the startingmaterials are in the range of 0.1 to 9 mol/L, preferably 0.2 to 5 mol/L,for the titanium(IV) compound and in the range of 0.01 to 1 mol/L,preferably 0.02 to 0.2 mol/L for the trialkyl aluminum compound. Thetitanium component is added to the aluminum component over a period of0.1 min to 60 min, preferably 1 min to 30 min, the molar ratio oftitanium and aluminum in the final mixture being in the range of 1:0.01to 1:4.

In another embodiment, a suitable catalyst system is obtained by a oneor two-step reaction of a titanium(IV) compound with a trialkyl aluminumcompound in an inert organic solvent at temperatures in the range of−40° C. to 200° C., preferably −20° C. to 150° C. In the first step thetitanium(IV) compound is reacted with the trialkyl aluminum compound attemperatures in the range of −40° C. to 100° C., preferably −20° C. to50° C. using a molar ratio of titanium to aluminum in the range of 1:0.1to 1:0.8. The concentrations of the starting materials are in the rangeof 0.1 to 9.1 mol/L, preferably 5 to 9.1 mol/L, for the titanium(IV)compound and in the range of 0.05 and 1 mol/L, preferably 0.1 to 0.9mol/L for the trialkyl aluminum compound. The titanium component isadded to the aluminum compound over a period of 0.1 min to 800 min,preferably 30 min to 600 min. In a second step, if applied, the reactionproduct obtained in the first step is treated with a trialkyl aluminumcompound at temperatures in the range of −10° C. to 150° C., preferably10° C. to 130° C. using a molar ratio of titanium to aluminum in therange of 1:0.01 to 1:5.

In yet another embodiment, a suitable catalyst system is obtained by aprocedure wherein, in a first reaction stage, a magnesium alcoholate isreacted with a titanium chloride in an inert hydrocarbon at atemperature of 50° to 100° C. In a second reaction stage the reactionmixture formed is subjected to heat treatment for a period of about 10to 100 hours at a temperature of 110° to 200° C. accompanied byevolution of alkyl chloride until no further alkyl chloride is evolved,and the solid is then freed from soluble reaction products by washingseveral times with a hydrocarbon.

In a further embodiment, catalysts supported on silica, such as forexample the commercially available catalyst system Sylopol 5917 can alsobe used.

Using such catalyst systems, the polymerization is normally carried outin suspension at low pressure and temperature in one or multiple steps,continuous or batch. The polymerization temperature is typically in therange of 30° C. to 130° C., preferably is the range of 50° C. and 90° C.and the ethylene partial pressure is typically less than 10 MPa,preferably 0.05 and 5 MPa. Trialkyl aluminums, like for example but notlimited to isoprenyl aluminum and triisobutyl aluminum, are used asco-catalyst such that the ratio of Al:Ti (co-catalyst versus catalyst)is in the range of 0.01 to 100:1, more preferably is the range of 0.03to 50:1. The solvent is an inert organic solvent as typically used forZiegler type polymerizations. Examples are butane, pentane, hexane,cyclohexene, octane, nonane, decane, their isomers and mixtures thereof.The polymer molecular mass is controlled through feeding hydrogen. Theratio of hydrogen partial pressure to ethylene partial pressure is inthe range of 0 to 50, preferably the range of 0 to 10. The polymer isisolated and dried in a fluidized bed drier under nitrogen. The solventmay be removed through steam distillation in case of using high boilingsolvents. Salts of long chain fatty acids may be added as a stabilizer.Typical examples are calcium, magnesium and zinc stearate.

Optionally, other catalysts such as Phillips catalysts, metallocenes andpost metallocenes may be employed. Generally a cocatalyst such asalumoxane or alkyl aluminum or alkyl magnesium compound is alsoemployed. Other suitable catalyst systems include Group 4 metalcomplexes of phenolate ether ligands.

In accordance with the present disclosure, the polyethylene polymer isformed into particles and combined with a plasticizer. In oneembodiment, the polyethylene particles are made from a polyethylenepolymer having a relatively low bulk density as measured according toDIN53466. For instance, in one embodiment, the bulk density is generallyless than about 0.4 g/cm³, such as less than about 0.35 g/cm³, such asless than about 0.33 g/cm³, such as less than about 0.3 g/cm³, such asless than about 0.28 g/cm³, such as less than about 0.26 g/cm³. The bulkdensity is generally greater than about 0.1 g/cm³, such as greater thanabout 0.15 g/cm³. In one embodiment, the polymer has a bulk density offrom about 0.2 g/cm³ to about 0.27 g/cm³.

In one embodiment, the polyethylene particles can be a free-flowingpowder. The particles can have a median particle size (d50) of less than200 microns. For example, the median particle size (d50) of thepolyethylene particles can be less than about 150 microns, such as lessthan about 100 microns. The median particle size (d50) is generallygreater than about 60 microns. The powder particle size can be measuredutilizing a laser diffraction method according to ISO 13320.

In one embodiment, 90% of the polyethylene particles can have a particlesize of less than about 250 microns. In other embodiments, 90% of thepolyethylene particles can have a particle size of less than about 200microns, such as less than about 170.

The molecular weight of the polyethylene polymer can vary depending uponthe particular application. The polyethylene polymer, for instance, mayhave an average molecular weight, as determined according to theMargolies equation. The molecular weight can be determined by firstmeasuring the viscosity number according to DIN EN ISO Test 1628. Drypowder flow is measured using a 25 mm nozzle. The molecular weight isthen calculated using the Margolies equation from the viscosity numbers,of at least or greater than about 500,000 g/mol, such as greater thanabout 1,000,000 g/mol, such as greater than about 1,500,000 g/mol, suchas greater than about 2,000,000 g/mol, such as greater than about2,500,000 g/mol, such as greater than about 3,000,000 g/mol, such asgreater than about 3,500,000 g/mol, such as greater than about 4,000,000g/mol. The average molecular weight is generally less than about12,000,000 g/mol, such as less than about 10,000,000.

The polyethylene may have a viscosity number of from at least 100 mL/g,such as at least 500 mL/g, such as at least 1,500 mL/g, such as at least2,000 mL/g, such as at least 4,000 mL/g to less than about 6,000 mL/g,such as less than about 5,000 mL/g, such as less than about 4000 mL/g,such as less than about 3,000 mL/g, such as less than about 1,000 mL/g,as determined according to ISO 1628 part 3 utilizing a concentration indecahydronapthalene of 0.0002 g/mL.

The polyethylene may have a crystallinity of from at least about 40% to85%, such as from 45% to 80%.

In order to form polymer articles through a gel spinning or extrudingprocess, the polyethylene particles as described above are combined withthe acid scavenger and a plasticizer to form a polymer composition. Ingeneral, the polyethylene particles are present in the polymercomposition in an amount up to about 50% by weight. For instance, thepolyethylene particles can be present in the polymer composition in anamount less than about 45% by weight, such as in an amount less thanabout 40% by weight, such as in an amount less than about 35% by weight,such as in an amount less than about 30% by weight, such as in an amountless than about 25% by weight, such as in an amount less than about 20%by weight, such as in an amount less than about 15% by weight, such asin an amount less than about 10% by weight, such as in an amount lessthan about 5% by weight. The polyethylene particles can be present inthe composition in an amount greater than about 1% by weight, such as inan amount greater than about 3% by weight, such as in an amount greaterthan about 5% by weight, such as in an amount greater than about 10% byweight, such as in an amount greater than about 15% by weight, such asin an amount greater than about 20% by weight, such as in an amountgreater than about 25% by weight. During gel processing, the plasticizercan be substantially or completely removed in forming polymer articles.For example, in one embodiment, the resulting polymer article cancontain the polyethylene polymer in an amount greater than about 70% byweight, such as in an amount greater than about 80% by weight, such asin an amount greater than about 85% by weight, such as in an amountgreater than about 90% by weight, such as in an amount greater thanabout 95% by weight, such as in an amount greater than about 98% byweight, such as in an amount greater than about 99% by weight.

Because the acid scavenger is generally insoluble in the plasticizerand/or any extraction solvents used during the process, the acidscavenger remains in the polymer article formed from the polyethylenepolymer. Thus, polymer articles made in accordance with the presentdisclosure can contain one or more acid scavengers in accordance withthe present disclosure in an amount greater than about 10 ppm, such asin an amount greater than about 20 ppm, such as in an amount greaterthan about 30 ppm and generally in an amount less than about 250 ppm,such as in an amount less than about 150 ppm on a weight basis.

In general, any suitable plasticizer can be combined with thepolyethylene particles as long as the plasticizer is capable of forminga gel-like material suitable for gel spinning or extruding. Theplasticizer, for instance, may comprise a hydrocarbon oil, an alcohol,an ether, an ester such as a diester, or mixtures thereof. For instance,suitable plasticizers include mineral oil, a paraffinic oil, decaline,and the like. Other plasticizers include xylene, dioctyl phthalate,dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonylalcohol, diphenyl ether, n-decane, n-dodecane, octane, nonane, kerosene,toluene, naphthalene, tetraline, and the like. In one embodiment, theplasticizer may comprise a halogenated hydrocarbon, such asmonochlorobenzene. Cycloalkanes and cycloalkenes may also be used, suchas camphene, methane, dipentene, methylcyclopentandiene, tricyclodecane,1,2,4,5-tetramethyl-1,4-cyclohexadiene, and the like. The plasticizermay comprise mixtures and combinations of any of the above as well.

The plasticizer is generally present in the composition used to form thepolymer articles in an amount greater than about 50% by weight, such asin an amount greater than about 55% by weight, such as in an amountgreater than about 60% by weight, such as in an amount greater thanabout 65% by weight, such as in an amount greater than about 70% byweight, such as in an amount greater than about 75% by weight, such asin an amount greater than about 80% by weight, such as in an amountgreater than about 85% by weight, such as in an amount greater thanabout 90% by weight, such as in an amount greater than about 95% byweight, such as in an amount greater than about 98% by weight. In fact,the plasticizer can be present in an amount up to about 99.5% by weight.

The polyethylene particles blend with the plasticizer to form ahomogeneous gel-like material.

In order to form polymer articles in accordance with the presentdisclosure, the polyethylene particles are combined with the acidscavenger and the plasticizer and extruded through a die of a desiredshape. In one embodiment, the composition can be heated within theextruder. For example, the plasticizer can be combined with thepolyethylene particles and fed into an extruder. In accordance with thepresent disclosure, the plasticizer and polyethylene particles form ahomogeneous gel-like material prior to leaving the extruder for formingpolymer articles with little to no impurities.

In one embodiment, elongated articles are formed during the gel spinningor extruding process. The polymer article, for instance, may be in theform of a fiber, a film, or a membrane.

During the process, at least a portion of the plasticizer is removedfrom the final product. The plasticizer removal process may occur due toevaporation when a relatively volatile plasticizer is used. Otherwise,an extraction liquid can be used to remove the plasticizer. Theextraction liquid may comprise, for instance, a hydrocarbon solvent. Oneexample of the extraction liquid, for instance, is dichloromethane. Inaccordance with the present disclosure, the acid scavenger is bothinsoluble in the plasticizer and the extraction solvent. In oneembodiment, evaporation and extraction are both used.

If desired, the resulting polymer article can be stretched at anelevated temperature below the melting point of the polyethylene polymerto increase strength and modulus. Suitable temperatures for stretchingare in the range of from about ambient temperature to about 155° C. Thedraw ratios can generally be greater than about 4, such as greater thanabout 6, such as greater than about 8, such as greater than about 10,such as greater than about 15, such as greater than about 20, such asgreater than about 25, such as greater than about 30. In certainembodiments, the draw ratio can be greater than about 50, such asgreater than about 100, such as greater than about 110, such as greaterthan about 120, such as greater than about 130, such as greater thanabout 140, such as greater than about 150. Draw ratios are generallyless than about 1,000, such as less than about 800, such as less thanabout 600, such as less than about 400. In one embodiment, lower drawratios are used such as from about 4 to about 10. The polymer articlecan be uniaxially stretched or biaxially stretched.

Polymer articles made in accordance with the present disclosure havenumerous uses and applications. For example, in one embodiment, theprocess is used to produce a membrane. The membrane can be used, forinstance, as a battery separator. Alternatively, the membrane can beused as a microfilter. When producing fibers, the fibers can be used toproduce nonwoven fabrics, ropes, nets, and the like. In one embodiment,the fibers can be used as a filler material in ballistic apparel.

The polymer composition and polymer articles made in accordance with thepresent disclosure may contain various other additives, such as heatstabilizers, light stabilizers, UV absorbers, flame retardants,lubricants, colorants, and the like.

In one embodiment, a heat stabilizer may be present in the composition.The heat stabilizer may include, but is not limited to, phosphites,aminic antioxidants, phenolic antioxidants, or any combination thereof.

In one embodiment, an antioxidant may be present in the composition. Theantioxidant may include, but is not limited to, secondary aromaticamines, benzofuranones, sterically hindered phenols, or any combinationthereof.

In one embodiment, a light stabilizer may be present in the composition.The light stabilizer may include, but is not limited to,2-(2′-hydroxyphenyl)-benzotriazoles, 2-hydroxy-4-alkoxybenzophenones,nickel containing light stabilizers,3,5-di-tert-butyl-4-hydroxbenzoates, sterically hindered amines (HALS),or any combination thereof.

In one embodiment, a UV absorber may be present in the composition inlieu of or in addition to the light stabilizer. The UV absorber mayinclude, but is not limited to, a benzotriazole, a benzoate, or acombination thereof, or any combination thereof.

In one embodiment, a halogenated flame retardant may be present in thecomposition. The halogenated flame retardant may include, but is notlimited to, tetrabromobisphenol A (TBBA), tetrabromophthalic acidanhydride, dedecachloropentacyclooctadecadiene (dechlorane),hexabromocyclodedecane, chlorinated paraffins, or any combinationthereof.

In one embodiment, a non-halogenated flame retardant may be present inthe composition. The non-halogenated flame retardant may include, but isnot limited to, resorcinol diphosphoric acid tetraphenyl ester (RDP),ammonium polyphosphate (APP), phosphine acid derivatives, friarylphosphates, trichloropropylphosphate (TCPP), magnesium hydroxide,aluminum trihydroxide, antimony trioxide.

In one embodiment, a lubricant may be present in the composition. Thelubricant may include, but is not limited to, silicone oil, waxes,molybdenum disulfide, or any combination thereof.

In one embodiment, a colorant may be present in the composition. Thecolorant may include, but is not limited to, inorganic and organic basedcolor pigments.

These additives may be used singly or in any combination thereof. Ingeneral, unless stated otherwise, if the additives are utilized, theymay be present in an amount of at least about 0.05 wt. %, such as atlast about 0.1 wt. %, such as at least about 0.25 wt. %, such as atleast about 0.5 wt. %, such as at least about 1 wt. % and generally lessthan about 20 wt. %, such as less than about 10 wt. %, such as less thanabout 5 wt. %, such as less than about 4 wt. %, such as less than about2 wt. %. The sum of the wt. % of all of the components, including anyadditives if present, utilized in the polymer composition will be 100wt. %.

The present disclosure may be better understood with reference to thefollowing example. The following example is given below by way ofillustration and not by way of limitation. The following experimentswere conducted in order to show some of the benefits and advantages ofthe present invention.

Example 1

Various different polymer compositions were formulated containing highdensity polyethylene particles, a plasticizer, and an acid scavenger.Acid scavengers made in accordance with the present disclosure werecompared with the use of calcium stearate as an acid scavenge.

More particularly, the acid scavenger, calcium stearate, was comparedwith the use of magnesium aluminum hydroxide carbonates obtained fromdifferent commercial sources. For instance, the magnesium aluminumhydroxide carbonates tested included HYCITE 713 obtained from Clariant,DHT-4A obtained from Kisuma Chemical, and DHT-4A-2 also obtained fromKisuma Chemical. HYCITE 713 has a magnesium oxide to aluminum oxide moleratio of from about 4 to about 5 mol/mol. DHT-4A has a magnesium oxideto aluminum oxide ratio of 4.3 mol/mol. DHT-4A-2 is the dehydrated formof DHT-4A.

The above acid scavengers were combined with polyethylene particles. Thepolyethylene particles had a molecular weight of 700,000 g/mol and had aD50 particle size of 115 micrometers.

The blended formulations containing the different acid scavengers werethen tested for acid release. In particular, the polymer compositionswere heated to a temperature which triggers the release of hydrochloricacid. After a certain amount of time, the amount of hydrochloric acidreleased from the sample was determined using the gas detecting systemavailable from Draeger Safety AG & Co. KGaA. Any detection ofhydrochloric acid indicated an insufficient amount of acid scavengerpresent.

The following results were obtained:

Acid HCl release scavenger during Loading Draegertest Sample No. Acidscavenger type in ppm in ppm 1 none none 2.5 2 Calcium Stearate 200 0.23 Calcium Stearate 500 0 4 Magnesium aluminum 75 0 hydroxide carbonate(MgO/Al₂O₃ = 4-5 mol/mol) 5 Magnesium aluminum 50 0 hydroxide carbonate(MgO/Al₂O₃ = 4-5 mol/mol) 6 Magnesium aluminum 75 0 hydroxide carbonate(MgO/Al₂O₃ = 4.3 mol/mol) 7 Magnesium aluminum 50 0 hydroxide carbonate(MgO/Al₂O₃ = 4.3 mol/mol) 8 Magnesium aluminum 75 0 hydroxide carbonatedehydrated (MgO/Al₂O₃ = 4.3 mol/mol) 9 Magnesium aluminum 50 0.1hydroxide carbonate dehydrated (MgO/Al₂O₃ = 4.3 mol/mol)

As shown above, the acid scavengers of the present disclosure arecapable of preventing acid release at unexpectedly low concentrations.Although unknown, it is believed that the acid scavengers of the presentdisclosure synergistically blend with the polyethylene particles and theplasticizer during polymer processing to improve the efficiency of thechemical compound.

Example 2

The following example demonstrates the corrosion resistant properties ofcompositions made in accordance with the present disclosure.

Carbon steel type 1.1274 was coated with various different polymercompositions that were formulated containing high density polyethyleneparticles and an acid scavenger. Acid scavengers in accordance with thepresent disclosure were compared with the use of calcium stearate.

Carbon steel strips having dimensions of 0.2 mm thick, 10 mm wide, and50 mm long were tested. The carbon steel samples were initially cleanedwith acetone and weighted before being placed in a compression moldtogether with 100 g of a polymer formulation, followed by being heatedfor 50 minutes to a temperature of 250° C. at a pressure of 5 bars. Thesamples were then allowed to cool and placed in water vapor for onehour. They were weighted once more after drying.

Each polymer formulation contained an acid scavenger. The acidscavenger, calcium stearate, was compared with a hydrotalcite. Thehydrotalcite (magnesium aluminum hydroxide carbonate) tested was DHT-4Aobtained from Kisuma Chemical. DHT-4A has a magnesium oxide to aluminumoxide mole ratio of 4.3 mol/mol.

The above acid scavengers were combined with polyethylene particles anda plasticizer in an amount ranging from 0 to 1000 ppm. The polyethyleneparticles have a molecular weight of 700,000 g/mol (Margolies' Equation)and had a D₅₀ particle size of 115 micrometers.

The following results were obtained:

Loading of Acid Scavenger Average weight Base Resin Additive in ppmSteel type % increase UHMW None 0 1.1274 0.2253 Polyethylene C-SteelUHMW Ca—St 200 1.1274 0.1115 Polyethylene C-Steel UHMW Ca—St 500 1.12740.0424 Polyethylene C-Steel UHMW Ca—St 700 1.1274 0.0182 PolyethyleneC-Steel UHMW Ca—St 700 1.1274 0.0290 Polyethylene C-Steel UHMW Ca—St1000 1.1274 0.0261 Polyethylene C-Steel UHMW Hydrotalcite 100 1.12740.1546 Polyethylene C-Steel UHMW Hydrotalcite 150 1.1274 0.0373Polyethylene C-Steel UHMW Hydrotalcite 200 1.1274 0.0090 PolyethyleneC-Steel

As shown above, much less hydrotalcite is needed for corrosionprotection. In addition, the hydrotalcite provided greater corrosionprevention.

Example 3

The following example was conducted to demonstrate that polymercompositions made in accordance with the present disclosure produce lessextractables in comparison to calcium stearate when contacted withdichloromethane.

Various different polymer compositions were formulated and gel extrudedcontaining high density polyethylene particles and an acid scavenger.Dichloromethane was used as an extracting solvent after the moldingprocess. Acid scavengers made in accordance with the present disclosurewere compared with the use of calcium stearate.

More particularly, the acid scavenger, calcium stearate, was comparedwith the use of magnesium aluminum hydroxide carbonates obtained fromdifferent commercial sources. In the present example, the magnesiumaluminum hydroxide carbonates tested included HYCITE 713 obtained fromClariant, and DHT-4A obtained from Kisuma Chemical. HYCITE 713 has amagnesium oxide to aluminum oxide mole ratio of from about 4 to about 5mol/mol. DHT-4A has a magnesium oxide to aluminum oxide ratio of 4.3mol/mol.

The above acid scavengers were combined with polyethylene particles inan amount ranging from 0 to 500 ppm. Calcium stearate was combined withpolyethylene particles having a molecular weight of 600,000 g/mol and aD50 particle size of 110 microns. The hydrotalcite additives werecombined with a polyethylene having a molecular weight of 1,700,000g/mol and a D50 particle size of 135 microns.

The amount of additive in each polymer composition was measured afterextraction. The following results were obtained:

Type of PPM of % of additive remaining Resin additive additive in resinafter extraction UHMW Polyethylene Hydrotalcite¹ 110 94 UHMWPolyethylene Hydrotalcite² 110 89 UHMW Polyethylene Ca—St 500 79 UHMWPolyethylene Ca—St 500 79 ¹magnesium oxide to aluminum oxide ratio of4.3 mol/mol ²magnesium oxide to aluminum oxide mol ratio of from about 4to about 5 mol/mol

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention, which ismore particularly set forth in the appended claims. In addition, itshould be understood that aspects of the various embodiments may beinterchanged both in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing descriptions is byway of example only, and is not intended to limit the invention sofurther described in such appended claims.

1-20. (canceled)
 21. A polymer membrane or fiber comprising: a highdensity polyethylene combined with an acid scavenger, the acid scavengercomprising an inorganic compound, the inorganic compound comprising anoxide, a carbonate, a silicate, or mixtures thereof, and wherein theacid scavenger is present in the polymer membrane or fiber in an amountless than about 500 ppm on a weight basis.
 22. A polymer membrane orfiber as defined in claim 21, wherein the acid scavenger comprises acarbonate.
 23. A polymer membrane or fiber as defined in claim 21,wherein the acid scavenger comprises a hydrotalcite.
 24. A polymermembrane or fiber as defined in claim 21, wherein the acid scavenger ispresent in the membrane or fiber in an amount less than about 250 ppm ona weight basis.
 25. A polymer membrane or fiber as defined in claim 21,wherein the acid scavenger is present in the membrane or fiber in anamount less than about 150 ppm on a weight basis.
 26. A polymer membraneor fiber as defined in claim 21, wherein the acid scavenger is presentin the membrane or fiber in an amount less than about 100 ppm on aweight basis.
 27. A polymer membrane or fiber as defined in claim 21,wherein the high density polyethylene is present in the composition inan amount greater than about 85% by weight.
 28. A polymer membrane orfiber as defined in claim 21, wherein the high density polyethylene ispresent in the composition in an amount greater than about 95% byweight.
 29. A polymer membrane or fiber as defined in claim 21, whereinthe high density polyethylene has a molecular weight of greater thanabout 500,000 g/mol and less than about 10,000,000 g/mol.
 30. A polymermembrane or fiber as defined in claim 21, wherein the high densitypolyethylene has a molecular weight of greater than about 1,000,000g/mol and less than about 10,000,000 g/mol.
 31. A polymer membrane orfiber as defined in claim 21, wherein the high density polyethylene hasa molecular weight of greater than about 2,000,000 g/mol and less thanabout 10,000,000 g/mol.
 32. A polymer membrane or fiber as defined inclaim 21, wherein the high density polyethylene is a Ziegler-Nattacatalyzed ultrahigh molecular weight polyethylene.
 33. A polymermembrane or fiber as defined in claim 21, wherein the membrane or fiberfurther comprises a plasticizer.
 34. A polymer membrane or fiber asdefined in claim 33, wherein the plasticizer comprises mineral oil, aparaffinic oil, a hydrocarbon, an alcohol, an ether, an ester, ormixtures thereof.
 35. A polymer membrane or fiber as defined in claim33, wherein the plasticizer comprises decaline, xylene, dioctylphthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decylalcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, octane,nonane, kerosene, toluene, naphthalene, tetraline, monochlorobenzene,camphene, methane, dipentene, methylcyclopentandiene, tricyclodecane,1,2,4,5-tetramethyl-1,4-cyclohexadiene, or mixtures thereof.
 36. Apolymer membrane or fiber as defined in claim 21 comprising a membrane.37. A battery separator comprising the membrane of claim
 36. 38. Abattery comprising the battery separator of claim 37.